The supply of therapeutic oxygen to patients in homes and other residential settings is an important and growing segment of the health care industry. Oxygen can be supplied to a patient by liquid or compressed oxygen with an appropriate vaporization or pressure regulation system and a gas delivery cannula. Alternatively, oxygen can be supplied by the generation of oxygen using a small on site air separation device located near the patient which delivers the generated oxygen via a cannula. This latter mode of oxygen supply is preferred by many patients and numerous small air separation devices have been developed in response to this demonstrated need.
Respiratory oxygen usage rates typically range up to 3 LPM (liters per minute at 22° C. and 1 atma pressure) for ambulatory patients with relatively low oxygen requirements, up to 5 LPM for patients with more serious respiratory problems and possibly limited mobility, and in certain cases up to 10 LPM for those with the most serious respiratory problems and more limited mobility. A patient initially may require a higher oxygen supply rate during an illness and later may require less oxygen as recovery is achieved. Alternatively, a patient may require increasing oxygen rates as a chronic condition worsens. Patient oxygen requirements thus are highly variable, and the maximum oxygen requirement may be three to five times the minimum oxygen requirement.
Residential or home oxygen generation systems therefore must be designed for a wide range of oxygen production rates in order to meet these diverse patient requirements. A provider of home oxygen generators typically will prefer to limit the number of different systems offered for sale while still meeting patient requirements. The economic design of small oxygen generation systems with high turndown ratios is difficult, and it may be necessary for a provider to offer several sizes of generators to meet patient needs. It is desirable for economic reasons to minimize the number of oxygen generation system offerings and to maximize the turndown ratio of each system offered. In addition, it is desirable to meet both ambulatory and non-ambulatory oxygen requirements with a single generator system when possible.